Safe rackmountable storage enclosure

ABSTRACT

A storage enclosure includes a chassis, a plurality of drawers, and one or more power supplies. The plurality of drawers each include up to a predetermined number of storage devices. The plurality of drawers is individually extendable up to a predetermined distance through a front surface of the chassis. When each drawer of the plurality of drawers comprises the predetermined number of storage devices and is extended the predetermined distance through the front surface of the chassis, the center of mass of the storage enclosure is behind the front surface of the chassis.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is related to copending non-Provisional U.S.application Ser. No. 13/747,585, filed Jan. 23, 2013, entitled HIGHDENSITY DATA STORAGE SYSTEM WITH IMPROVED STORAGE DEVICE ACCESS(inventors Brenden Michael Rust and Charles Powell Morris), copendingnon-Provisional U.S. application Ser. No. 13/747,609, filed Jan. 23,2013, entitled STORAGE ENCLOSURE WITH INDEPENDENT STORAGE DEVICE DRAWERS(inventors Victor Key Pecone, Kevin James Lonergan, Brenden MichaelRust, and George Alexander Kalwitz), and copending non-Provisional U.S.application Ser. No. 13/747,637, filed Jan. 23, 2013, entitled STORAGEDEVICE CARRIER FOR HIGH DENSITY STORAGE SYSTEM (inventor David MichaelKeffeler).

FIELD

The present invention is directed to computer data storage systems. Inparticular, the present invention is directed to high-density storageenclosures and methods for methods for safe installation, removal, andrepair of high-density rackmountable storage enclosures.

BACKGROUND

In data storage systems, data storage density is always increasing inresponse to market demand for increased data storage. Each newgeneration of storage devices increases storage density over previousgenerations of storage devices, and often in more compact form factors.For example, current enterprise 3.5″ hard disk drives are presentlyavailable in 2 TB and 3 TB capacities, while 2.5″ hard disk drives arepresently available in 1 TB capacities. Additionally, storage subsystemsare being designed to store increasing numbers of storage devices. Forexample, commercial storage systems are currently available that canstore up to 60 storage devices in a 4 rack unit high (4U) rackmountableenclosure.

Traditionally, rackmountable storage enclosures utilize front access,where each storage device is individually mounted to a sled and isinserted or removed from the storage enclosure front. For example,conventional storage enclosures of this arrangement could mount 12 3.5″storage devices in a 2U enclosure, 16 3.5″ storage devices in a 3Uenclosure, or 25 2.5″ storage devices in a 2U enclosure.

High-density storage systems include relatively large numbers of storagedevices. In one approach of high-density storage systems, density hasbeen increased by allowing multiple storage devices to be mounted oneach front-accessible sled. In some cases, the sleds are wider than asingle storage device, sometimes up to the total internal width of arackmountable shelf. In other cases, the sleds are deeper. In mostcases, the storage devices are usually accessed through the top of asled, after the sled has been pulled out from the front of the storageenclosure. Some high-density storage systems arrange storage devices onboth sides of a drawer, where some storage devices of the same drawerare accessed from the left side, and other storage devices are accessedfrom the right side.

It has been found in recent years that increased numbers of storagedevices can be mounted in a single high density storage system byutilizing a “tombstone” storage device mounting approach. A “tombstone”storage system mounts all storage devices vertically on-end in an arrayof rows and columns, where top access is required for all storagedevices. In order to access a storage device in a “tombstone” system, adrawer mounting storage devices of the high-density storage system isusually slid forward on rails. The drawer must be slid forward farenough so that a top cover exposing all storage devices may be removed.A user or system administrator then stands over the top of the drawerand performs any necessary maintenance operation with the storagedevices. Although the “tombstone” approach is very space efficient andcan mount a large number of storage devices, it has severaldisadvantages. First, “tombstone” high density storage systems areusually quite heavy and difficult for one or two people to install.Strong slides and mounting structures are required so the entire drawermay be entirely slid forward. Second, “tombstone” storage systemsrequire top access. In some cases, this requires a ladder or otherdevice so that a person can get over the top of the enclosure andservice the storage enclosure accordingly. Third, when the storagedevice drawer is slid forward, the entire weight of the drawer isforward of the rack rails of the rack the system is mounted within,possibly making the entire rack unstable and able to tip over.

SUMMARY

The present invention is directed to solving disadvantages of the priorart. In accordance with embodiments of the present invention, a storageenclosure is provided. The storage enclosure includes a chassis, aplurality of drawers, and one or more power supplies. The plurality ofdrawers each include up to a predetermined number of storage devices.The plurality of drawers is individually extendable up to apredetermined distance through a front surface of the chassis. When eachdrawer of the plurality of drawers comprises the predetermined number ofstorage devices and is extended the predetermined distance through thefront surface of the chassis, the center of mass of the storageenclosure is behind the front surface of the chassis.

In accordance with other embodiments of the present invention, a storageenclosure for safe mounting in a 19″ rack is provided. The storageenclosure includes one or more drawers of a left drawer configuration,one or more drawers of a right drawer configuration, one or more storagecontroller modules, and one or more power supplies. The one or moredrawers of the left drawer configuration allow storage devices to beinserted or removed only from the right side of the drawer and the oneor more drawers of the right drawer configuration allow storage devicesto be inserted or removed only from the left side of the drawer. Each ofthe one or more storage controller modules include a storage controllerfor controlling one or more storage devices of the one or more drawersof the left drawer and right drawer configuration. The one or more powersupplies provide DC power to the one or more drawers of the left drawerand right drawer configuration and the one or more storage controllermodules. When each of the drawers of the left drawer and right drawerconfigurations are fully populated with storage devices and is fullyextended from the front surface of the chassis, the center of mass ofthe storage enclosure is between the front surface and the rear surfaceof the chassis.

An advantage of the present invention is that it provides for safeoperation and maintenance when mounted in a standard 19″ equipment rack.Each of a plurality of storage device drawers is able to be extended upto a predetermined distance from the front surface of the storageenclosure chassis. When all drawers are fully populated with storagedevices and all drawers are extended the predetermined distance from thechassis, the center of mass of the storage enclosure is behind the frontrails of the equipment rack. Therefore, a moment is not created thatwould contribute to the equipment rack tipping over, thereby enhancingsafe operation for users and system administrators.

Another advantage of the present invention is it is able to be installedor removed safely from a standard 19″ equipment rack. The storageenclosure of the present invention includes various modules. The modulesinclude power supplies, storage controller modules, and drawers. None ofthe modules, even when fully populated with sub-components includingstorage devices, weighs more than 15 lbs. Therefore, a single user orsystem administrator may safely remove, install, or replace any modulewithout incurring a safety hazard due to module weight. Additionally,the fully populated storage enclosure weights 80 lbs or less, which mayallow safe handling by two individuals and contributes to less totalweight in the equipment rack.

Yet another advantage of the present invention is that no modules of thestorage enclosure require top-level access to install, remove, replace,or conduct a maintenance operation. Specifically, the drawers includeonly side-accessible storage devices, and only side access from a singleside is required to install, remove, or replace any storage device in adrawer. In many cases, this eliminates the need for a ladder for a useror system administrator, which reduces or eliminates a falling safetyhazard.

Additional features and advantages of embodiments of the presentinvention will become more readily apparent from the followingdescription, particularly when taken together with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating components of a data storagenetwork in accordance with embodiments of the present invention.

FIG. 2 a is a block diagram illustrating components of a firsthost-based data storage system in accordance with embodiments of thepresent invention.

FIG. 2 b is a block diagram illustrating components of a first nonhost-based data storage system in accordance with embodiments of thepresent invention.

FIG. 2 c is a block diagram illustrating components of a secondhost-based data storage system in accordance with embodiments of thepresent invention.

FIG. 2 d is a block diagram illustrating components of a secondnon-host-based data storage system in accordance with embodiments of thepresent invention.

FIG. 3 a is a diagram illustrating a storage enclosure in accordancewith embodiments of the present invention.

FIG. 3 b is a diagram illustrating a storage enclosure chassis inaccordance with embodiments of the present invention.

FIG. 3 c is a diagram illustrating chassis components of a storageenclosure without drawers in accordance with embodiments of the presentinvention.

FIG. 3 d is a diagram illustrating chassis components of a storageenclosure including drawers in accordance with embodiments of thepresent invention.

FIG. 3 e is a diagram illustrating a storage enclosure with a leftdrawer extended in accordance with embodiments of the present invention.

FIG. 3 f is a diagram illustrating a storage enclosure with a leftdrawer extended in accordance with embodiments of the present invention.

FIG. 3 g is a diagram illustrating a storage enclosure with a centerdrawer extended in accordance with embodiments of the present invention.

FIG. 3 h is a diagram illustrating a storage enclosure with a leftdrawer extended in accordance with embodiments of the present invention.

FIG. 3 i is a diagram illustrating a storage enclosure with a rightdrawer extended in accordance with embodiments of the present invention.

FIG. 3 j is a diagram illustrating a storage enclosure right drawerconfiguration in accordance with embodiments of the present invention.

FIG. 4 a is a diagram illustrating left and right drawer configurationsin accordance with embodiments of the present invention.

FIG. 4 b is a diagram illustrating drawers and power supply modules inaccordance with embodiments of the present invention.

FIG. 4 c is a diagram illustrating a drawer storage device mountingconfiguration in accordance with embodiments of the present invention.

FIG. 4 d is a diagram illustrating detail A for a drawer storage devicemounting configuration in accordance with embodiments of the presentinvention.

FIG. 4 e is a diagram illustrating a storage controller module inaccordance with embodiments of the present invention.

FIG. 4 f is a diagram illustrating chassis and drawer midplanes inaccordance with embodiments of the present invention.

FIG. 4 g is a diagram illustrating a chassis cutaway side view inaccordance with embodiments of the present invention.

FIG. 5 a is a diagram illustrating a storage enclosure in a rack with nodrawers extended in accordance with embodiments of the presentinvention.

FIG. 5 b is a diagram illustrating a storage enclosure in a rack withall drawers extended in accordance with embodiments of the presentinvention.

FIG. 6 is a block diagram illustrating a storage enclosure in accordancewith embodiments of the present invention.

FIG. 7 is a block diagram illustrating a drawer midplane in accordancewith embodiments of the present invention.

FIG. 8 is a block diagram illustrating a drawer interconnection to astorage enclosure in accordance with embodiments of the presentinvention.

FIG. 9 is a block diagram illustrating storage enclosure DC powerdistribution in accordance with embodiments of the present invention.

FIG. 10 a is a flowchart illustrating a drawer installation process inaccordance with embodiments of the present invention.

FIG. 10 b is a flowchart illustrating a drawer removal process inaccordance with embodiments of the present invention.

FIG. 11 a is a diagram illustrating a mounted storage device inaccordance with embodiments of the present invention.

FIG. 11 b is a diagram illustrating a stack of (4) mounted storagedevices in accordance with embodiments of the present invention.

FIG. 12 a is a diagram illustrating a front view of a storage devicecarrier left side in accordance with embodiments of the presentinvention.

FIG. 12 b is a diagram illustrating a rear view of a storage devicecarrier left side in accordance with embodiments of the presentinvention.

FIG. 13 a is a diagram illustrating a front view of a storage devicecarrier right side in accordance with embodiments of the presentinvention.

FIG. 13 b is a diagram illustrating a rear view of a storage devicecarrier right side in accordance with embodiments of the presentinvention.

DETAILED DESCRIPTION

The present inventors have observed various human factors engineeringproblems with high-density storage systems. High-density storage systemsprovide a storage enclosure containing large numbers of storage devices,where each storage device is not able to be individually inserted orremoved to or from the storage enclosure through the front surface ofthe storage enclosure. In a rackmountable storage enclosure that is 2rack units high (“2U”), a high-density storage system would thereforehave more than 12 3.5″ storage devices or 25 2.5″ storage devices. In arackmountable storage enclosure that is 3 rack units high (“3U”), ahigh-density storage system would therefore have more than 16 3.5″storage devices or 35 2.5″ storage devices.

In order to accommodate greater numbers of storage devices, high-densitystorage systems use other mounting arrangements for storage devices. Oneapproach is to use a “tombstone” storage enclosure, where all storagedevices are accessed through the top surface, after pulling arackmountable drawer including the storage enclosure forward such thatstorage device access is not blocked by the rack itself or anotherrackmountable module above the drawer containing the storage enclosure.A ladder is generally required to access the storage devices through thetop of the storage enclosure, since a user needs to see which storagedevice to physically remove or insert.

Another approach is to use a series of narrow front-accessible sleds,where each sled mounts a fixed number of storage devices. In some cases,storage devices are mounted in a “tandem” arrangement, where a longerstorage device carrier mounts 2, 3, or 4 storage devices. Thisarrangement often has a front storage device carrier profile that is thesame as a conventional storage device carrier mounting only a singlestorage device, and achieves high-density through greater depth ofstorage device mounting on a carrier, and possibly a deeper storageenclosure chassis.

Yet another approach is to use a series of wide side-accessible sleds,where each sled mounts a fixed number of storage devices. In some cases,each sled is the full width of the storage enclosure, and providesaccess to storage devices from both the left and the right sides.

These alternative packaging approaches for high-density storage systemsintroduce various human factor problems that negatively impact theaccessibility of storage devices or installation/removal safety ofmodules or the entire storage enclosure from a standard 19″ rack. Forexample, “tombstone” storage enclosures require top access to insert orremove any storage devices. In some cases, this requires a ladder inorder for service personnel to get above the storage enclosure,especially if the enclosure is mounted in the upper space of a tallrack. Additionally, “tombstone” storage enclosures are almost alwaysmounted on drawer slides, and the entire storage enclosure is pulledforward to provide top-level access. In addition to the possiblerequirement for a ladder, a safety factor is introduced since pullingthe storage enclosure forward moves a significant portion of storageenclosure mass forward of the rack rails, and may introduce a fronttip-over danger in a sparsely populated rack.

Although the present invention is described with respect to SAStechnology, it should be understood that the inventive aspects of thepresent invention apply to any such storage device interface technologyincluding but not limited to Fibre Channel, parallel SCSI, Parallel ATA,Serial ATA (SATA), or SSA.

Referring now to FIG. 1, a block diagram illustrating components of adata storage network 100 in accordance with embodiments of the presentinvention is shown. Data storage network 100 provides interconnectionbetween one or more host computers 108 and one or more storageenclosures 112. Network 104 includes networking communicationtechnologies suitable for high-volume data transfers between hostcomputers 108 and storage enclosures 112. Such technologies includeFiber Channel, Ethernet, SSA, SAS, iSCSI, Infiniband, ESCON, and FICON.Network 104 includes, but is not limited to local area networks (LANs)and storage area networks (SANs).

Host computers 108 execute application programs, and communicate withother host computers 108 or storage enclosures 112 through network 104.Storage enclosures 112 include storage devices that provide mass datastorage. Storage devices include hard disk drives, tape drives, opticaldrives, and solid state drives. In some embodiments, data storagenetwork 100 includes one or more management computers 116. Managementcomputers 116 monitor network 104, and provide error monitoring,configuration, and control functions. In most embodiments, managementcomputer 116 includes a graphical user interface (GUI) 120, throughwhich users or system administrators interact with management computer116. In some embodiments, management computer 116 interfaces withstorage enclosures 112 through network 104. In other embodiments,management computer 116 interfaces with storage enclosures 112 through adifferent connection or network other than network 104. Although threehost computers 108 a, 108 b, 108 c and three storage enclosures, 112 a,112 b, 112 c are shown in FIG. 1, network 104 includes any number ofhost computers 108 and storage enclosures 112.

Referring now to FIG. 2 a, a block diagram illustrating components of afirst host-based data storage system 200 incorporating a JBOD storageenclosure 224 in accordance with embodiments of the present invention isshown. The first host-based data storage system 200 includes one or morehost computers 108. Host computer 108 is generally a server, but couldalso be a desktop or mobile computer. Host computer 108 executesapplication programs that generate read and write requests to storagedevices 208 a-208 z. Host computer 108 includes one or more storagecontrollers 204, although only a single storage controller 204 isillustrated for clarity. In one embodiment, storage controller 204 is ahost bus adapter. In another embodiment, storage controller 204 is acontroller incorporating Redundant Array of Inexpensive Disks (RAID)technology. In yet another embodiment, storage controller 204 representsa pair of dual-redundant RAID controllers. Storage controller 204 mayeither be integrated on the motherboard of host computer 108, or may bean add-in board or other form of assembly in host computer 108. Storagecontroller 204 is well understood in the data storage art and is notlimited to any particular implementation or configuration.

Storage controller 204 transfers data to and from storage devices 208a-208 z in JBOD storage enclosure 224, over SAS links 220 and wide SASlink 216. In one embodiment, wide SAS link 216 includes 4 SAS lanes.JBOD storage enclosure 224 includes one or more SAS expanders 212, whichperform switching functions, and transfers data and commands betweenstorage controller 204 and storage devices 208 a-208 z. In general, thetransmit and receive paths of SAS links 220 to storage devices 208 aresingle lane SAS connections. However, in the future it is possible eachtransmit or receive path could be a multiple lane SAS link 216. Each SASlink 220 between SAS expander 212 and storage devices 208 includesseparate transmit and receive paths, and each storage device 208generally has two ports for independent interconnection to different SASexpanders 212 as illustrated in FIG. 6.

Referring now to FIG. 2 b, a block diagram illustrating components of afirst non host-based data storage system 232 incorporating a storageenclosure 112 in accordance with embodiments of the present invention isshown. Host computer 108 performs most of the functions previouslydescribed, although the “controller” or “storage controller” functionsare instead performed by storage controller 204 in storage enclosure112. Storage enclosure 112 of FIG. 2 b is therefore similar to JBODstorage enclosure 224 of FIG. 2 a, except that one or more storagecontrollers 204 are present in storage enclosure 112. Storage controller204 is described in more detail with respect to FIG. 6. In oneembodiment, storage controller 204 is a RAID controller. In anotherembodiment, storage controller 204 represents a pair of dual redundantRAID controllers. Host computer 108 communicates with storage enclosure112, including storage controller 204, over host bus or network 228.Host bus or network 228 is any suitable bus or network that allows highspeed data transfer between host computer 108 and storage controller204. Examples of host bus or network 228 include, but are not limitedto, SCSI, Fibre Channel, SSA, SCSI, SAS, iSCSI, Ethernet, Infiniband,ESCON, ATM, and FICON. In some embodiments, host bus or network 228 is astorage area network (SAN) or local area network (LAN).

Referring now to FIG. 2 c, a block diagram illustrating components of asecond host-based data storage system 240 incorporating JBOD storageenclosures 224 a, 224 b, and 224 c in accordance with embodiments of thepresent invention is shown. Second host-based data storage system 240 issimilar to first host-based data storage system 200 of FIG. 2 a, butadditional JBOD storage enclosures 224 b, 224 c are provided to supportadditional storage devices 208 c-208 f. In one embodiment, storagecontroller 204 is a host bus adapter. In another embodiment, storagecontroller 204 is a RAID controller. In yet another embodiment, storagecontroller 204 represents a pair of dual-redundant RAID controllers. Inorder to support additional JBOD storage enclosures 224 b, 224 c, SASexpanders 212 utilize daisy chain buses 236. Daisy chain bus 236utilizes the same protocol as SAS links 216, 220, and is generally a SASwide bus 216 having four SAS lanes. Daisy chain bus 236 a interconnectsSAS expander 212 a and SAS expander 212 b. Daisy chain bus 236 binterconnects SAS expander 212 b and SAS expander 212 c. Daisy chain bus236 c interconnects SAS expander 212 c and another storage enclosure112, in a similar fashion to daisy chain buses 236 a and 236 b.

In one embodiment, each JBOD storage enclosure 224 supports 48 storagedevices 208 and each storage controller 204 supports up to 128 storagedevices 208. However, in other embodiments each JBOD storage enclosure224 may support more or fewer than 48 storage devices 208, and eachstorage controller 204 may support more or fewer than 128 storagedevices 208.

Referring now to FIG. 2 d, a block diagram illustrating components of asecond non-host-based data storage system 244 in accordance withembodiments of the present invention is shown. Second non-host baseddata storage system 244 is similar to first non-host-based data storagesystem 232 of FIG. 2 b, but additional storage enclosures 112 b, 112 care provided to support additional storage devices 208 c-208 f. In oneembodiment, storage controller 204 is a RAID controller. In anotherembodiment, storage controller 204 represents a pair of dual redundantRAID controllers. In order to support additional storage enclosures 112b, 112 c, SAS expanders 212 utilize daisy chain buses 236. Daisy chainbuses 236 utilize the same protocol as SAS links 220, 216, and aregenerally a SAS wide bus 216 having four SAS lanes. Daisy chain bus 236a interconnects SAS expander 212 a and SAS expander 212 b. Daisy chainbus 236 b interconnects SAS expander 212 b and SAS expander 212 c. Daisychain bus 236 c interconnects SAS expander 212 c and another storageenclosure 112, in a similar fashion to daisy chain buses 236 a and 236b. In one embodiment, each storage enclosure 112 supports 48 storagedevices 208 and each storage controller 204 supports up to 128 storagedevices 208. However, in other embodiments each storage enclosure 112may support more or fewer than 48 storage devices 208, and each storagecontroller 204 may support more or fewer than 128 storage devices 208.

Referring now to FIG. 3 a, a diagram illustrating a storage enclosure112, 224 in accordance with embodiments of the present invention isshown. Storage enclosure 112,224 is a high-density storage system thatprovides storage for a large number of storage devices 208. In someembodiments, storage enclosure 112,224 is able to be mounted within a 19inch rack in conjunction with other similar or dissimilar modules. Inthe preferred embodiment, storage enclosure 112, 224 is two rack unitshigh. Storage enclosure 112, 224 includes a chassis 304, which isgenerally constructed of steel, aluminum, or other materials thatprovide appropriate strength, rigidity, and compatibility with EMI/EMCstandards. Chassis 304 has a top surface 308, a bottom surface 312, arear surface, a front surface, and two side surfaces.

In some embodiments, storage enclosure 112, 224 includes a front bezel316. The front bezel 316 is attached to the front surface of chassis304, and provides an aesthetic front cover for storage enclosure 112,224. The front bezel 316 includes finger grabs for user access withoutrequiring tools and some embodiments includes simple controls, such aspushbuttons, and LED or alphanumeric displays. Front bezel 316 alsoincludes various holes through which cooling air is drawn into chassis304 to cool storage devices 208 and other electronic assemblies ofstorage enclosure 112, 224.

Referring now to FIG. 3 b, a diagram illustrating a storage enclosurechassis 304 in accordance with embodiments of the present invention isshown. The chassis 304 includes chassis side surfaces 328. Chassis sidesurfaces 328 include a left side and a right side. The chassis 304 alsoincludes a chassis front surface 320, which the front bezel 316 attachesto and a plurality of storage device drawers are inserted or removedfrom the chassis. The chassis 304 further includes a chassis rearsurface 324, through which power supply 332 and storage controllermodules 336 are inserted or removed.

Referring now to FIG. 3 c, a diagram illustrating chassis components ofa storage enclosure 112 without drawers 352 in accordance withembodiments of the present invention is shown. FIG. 3 c illustrateschassis 304 of FIG. 3 b with the addition of a chassis midplane 340,power supplies 332, and storage controller module 336. The chassismidplane 340 provides electrical signal and power interconnectionbetween each of two redundant power supplies 332 a, 332 b, each of tworedundant storage controller modules 336, and drawers 352. Each of themodules in chassis 304 is designed for redundant operation.

Chassis 304 includes at least one drawer slide 348 for each of thedrawers 352 that mount the storage devices 208. Drawer slides 348provide a bearing surface for each drawer 352, allowing each drawer 352to be smoothly inserted or removed to or from chassis 304. Each of thedrawer slides 348 includes a mechanical latch hole 350, or otherlatching mechanism. Mechanical latch hole 350 mates with a mechanicallatch in the bottom surface of drawer 352, allowing drawer 352 to beremoved from chassis 304.

Storage enclosure 112 allows each drawer 352 to be fully operationalwhen the drawer 352 is fully extended through the front surface of thechassis 320. Therefore, it is necessary to provide flexible power andinterconnect signal cables between the chassis midplane 340 and eachdrawer 352. Drawer cable guides 344 are provided in chassis 304 toprotect the power and interconnect signal cables as a drawer 352 isbeing inserted or extended/removed from the chassis 304.

Referring now to FIG. 3 d, a diagram illustrating chassis components ofa storage enclosure 112 including drawers 352 in accordance withembodiments of the present invention are shown. FIG. 3 d illustrates thechassis 304 of FIG. 3 c with the addition of three drawers 352. Althoughonly a single storage controller module 336 is shown, in mostembodiments two such storage controller modules 336 would be present. Insome embodiments, the storage enclosure is a JBOD (Just a Bunch ofDisks) storage enclosure 224, and has no storage controller modules 336present.

Drawers 352 provide mounting for storage devices 208. Each drawer 352stores up to a predetermined number of storage devices 208 and thecomponents of each drawer 352 is described in later Figures. In thepreferred embodiment, each drawer 352 may store up to sixteen storagedevices 208. Each drawer 352 is mechanically independent of any otherdrawers 352 in the storage enclosure 112, 224. Mechanically independentmeans each drawer 352 may be added, removed, or extended from thechassis 304 regardless of the presence, absence, or extended position ofany other drawer 352.

Referring now to FIG. 3 e, a diagram illustrating a storage enclosure112, 224 with a left drawer 364 extended in accordance with embodimentsof the present invention is shown. Each drawer 352 is individuallyextendable or retractable from chassis 304. In one embodiment, only onedrawer 352 is extendable at the same time, and a mechanical and/orelectrical interlock system prevents more than one drawer 352 from beingextended at the same time. Mounted storage devices 368 each include asingle storage device 208, and each mounted storage device 368 may beindividually removed or inserted into left drawer 364 or any otherdrawer 352 of storage enclosure 112, 224. It should be noted that allmounted storage devices 368 of a left drawer 364 configuration areinserted or removed through the right side of the drawer 364.

Associated with each drawer 352, including left drawer 364, is a cablemanagement system 356. Cable management system 356 protects power andinterconnect signal cabling between the chassis midplane 340 and eachdrawer 352. In the preferred embodiment, cable management system 356includes a drawer cable guide 344 and a flexible cable chain 360. Theflexible cable chain 360 is provided for each drawer 352 and moveslinearly with left drawer 364 as the left drawer 364 is extended from orpushed into the storage enclosure 112, 224. Flexible cable chain 360 isconstructed in such a fashion as to limit any sideways movement of theflexible cable chain and allow only linear movement in concert with thedrawer 352 the flexible cable chain 360 is attached to. Power andinterconnect signal cables run within the drawer cable guide 344 and theflexible cable chain 360. In the preferred embodiment, the flexiblecable chain is IGUS part number 08-10-025-0 for the chain itself, and080-10-12 for the mounting end-links.

Referring now to FIG. 3 f, a diagram illustrating a storage enclosure112, 224 with a left drawer 364 extended in accordance with embodimentsof the present invention is shown. FIG. 3 f shows a left drawer 364extended from the storage enclosure 112, 224. With the left drawer 364extended, the cable management system 356 for the center drawer 372 ismore clearly visible in a retracted configuration.

Referring now to FIG. 3 g, a diagram illustrating a storage enclosure112, 224 with a center drawer 372 extended in accordance withembodiments of the present invention is shown. In the embodiment shownin FIG. 3 g, the center drawer 372 has the same mounted storage device368 configuration as the left drawer 364. The mounted storage device 368configuration refers to the side of a drawer 352 (left or right) throughwhich all mounted storage devices 368 are accessed. In otherembodiments, the mounted storage device 368 configuration of the centerdrawer 372 may be a right drawer 380 configuration.

A storage enclosure 112, 224 of the present invention may have no, one,or more than one center drawer 372. However, storage enclosure 112, 224includes at least one left drawer 364, and a least one right drawer 380.

Referring now to FIG. 3 h, a diagram illustrating a storage enclosure112 with a left drawer 364 extended in accordance with embodiments ofthe present invention is shown. FIG. 3 h illustrates left drawer 364extended a predetermined distance 376 from the chassis 304. Thepredetermined distance 376 is the distance the drawers 352 must beextended from the chassis 304 in order to access all mounted storagedevices 368 of a drawer 352. The predetermined distance 376 is the samefor all drawers 352 of a storage enclosure 112, 224, and in a preferredembodiment is 330 mm. When any drawer 352 is fully extended from thechassis 304, the drawer is extended the predetermined distance 376.

During normal operation, when a drawer 352 has not failed or is beingserviced, each drawer 352 remains fully functional when the drawer 352is fully extended from the chassis 304. Fully functional means one ormore power supplies 332 provide DC power to the fully extended drawer352 and each mounted storage device 368 in the drawer 352, andcommunication paths 828 are enabled between each mounted storage device368 and the chassis midplane 340.

Referring now to FIG. 3 i, a diagram illustrating a storage enclosure112, 224 with a right drawer 380 extended in accordance with embodimentsof the present invention is shown. The right drawer 380 includes a fixednumber of mounted storage devices 368, and is extendable the samepredetermined distance 376 as the other drawers 352 of storage enclosure112, 224. The right drawer 380 has a mirror image configuration comparedto the left drawer 364, as will be described with reference to FIG. 4 a.

Referring now to FIG. 3 j, a diagram illustrating a storage enclosureright drawer 380 configuration in accordance with embodiments of thepresent invention is shown. FIG. 3 j shows additional detail of theright drawer 380 configuration. The same details apply to other drawers352 of storage enclosure 112, 224. It should be noted that all mountedstorage devices 368 of a right drawer 380 configuration are inserted orremoved through the left side of the drawer 380.

The right drawer 380 includes a drawer chassis 388. The drawer chassis388 is a sheet metal assembly that supports mounted storage devices 368and other assemblies of the right drawer 380. Left drawers 364 andcenter drawers 372 also have a drawer chassis 388. Each mounted storagedevice 368 includes a storage device 208. However, not every bay in thedrawer chassis 388 for a mounted storage device 368 is necessarilypopulated with a storage device 208. For example, there may be only onemounted storage device 368 in a drawer 352, or even no mounted storagedevices 368 in a drawer 352. In the right drawer configuration of FIG. 3j, there are 16 mounted storage devices 368 present, organized as fourcolumns of four mounted storage devices 368 per column. In otherembodiments, there may be more than 16 or less than 16 mounted storagedevices 368 in a drawer 352, and mounted storage devices 368 may beorganized into different numbers of columns and mounted storage devices368 per column than shown. Each mounted storage device 368 isindependently insertable or removable to or from a drawer 352, andaccess does not depend on the position, presence, or absence of anyother mounted storage device 368 in the same drawer 352.

Referring now to FIG. 4 a, a diagram illustrating left and right drawer352 configurations in accordance with embodiments of the presentinvention is shown. In accordance with the present invention, leftdrawer 364 is of a left drawer configuration 404. A left drawerconfiguration 404 provides only right side access to mounted storagedevices 368. No mounted storage devices 368 are accessed through theleft side of a left drawer configuration 404.

In accordance with the present invention, right drawer 380 is of a rightdrawer configuration 408. A right drawer configuration 408 provides onlyleft side access to mounted storage devices 368. No mounted storagedevices 368 are accessed through the right side of a right drawerconfiguration 408.

As stated previously, any center drawer 372 may have a left drawerconfiguration 404 or right drawer configuration 408, and the presentinvention places no limitations on the number of center drawers 372 thatmay be present of the specific left/right configuration 404/408 of anycenter drawer 372.

Each drawer 352 of a left drawer configuration 404 or right drawerconfiguration 408 includes a drawer top 412, a drawer bottom 416, anddrawer indicators and controls 424. In some embodiments, drawers 352 mayhave a drawer pull 420 to facilitate insertion or removal of a drawer352. In some embodiments, the drawer bottom 416 includes a mechanicallatch that mates with a mechanical latch hole 350 of the chassis 304 aspreviously described.

Referring now to FIG. 4 b, a diagram illustrating drawers 352 and powersupply 332 modules in accordance with embodiments of the presentinvention is shown. Drawers 352 are as either a left drawerconfiguration 404 or a right drawer configuration 408, and include up toa fixed number of mounted storage devices 368. Power supplies 332receive external AC or DC power, and provide regulated DC power to thedrawers 352, storage controller modules 336, and chassis midplane 340.

Referring now to FIG. 4 c, a diagram illustrating a drawer storagedevice mounting configuration 404 in accordance with embodiments of thepresent invention is shown. Although a drawer 352 of the left drawerconfiguration 404 is illustrated, it should be understood that a drawer352 of the right drawer configuration 408 is the mirror image of theleft drawer configuration 404.

The drawer chassis 388 provides support and mounting for mounted storagedevices 368 and the drawer midplane 396. Detail A 428 is provided withadditional description in FIG. 4 d.

Referring now to FIG. 4 d, a diagram illustrating detail A for a drawerstorage device mounting configuration 404 in accordance with embodimentsof the present invention is shown. Drawer chassis 388 provides a mountedstorage device rail 432 on each side of a mounting bay for mountedstorage devices 368. The mounted storage device rail 432 providemechanical support for each mounted storage device 368, and allows amounted storage device 368 to be inserted or removed to or from thedrawer chassis 388 without interference. Mounting bays for mountedstorage devices 368 include a latching hole 436. The latching hole 436engages a carrier latch 1316 in the side of mounted storage device 368in order to lock the mounted storage device 368 into the mounting baywhen the mounted storage device 368 is fully inserted into the mountingbay.

Referring now to FIG. 4 e, a diagram illustrating a storage controllermodule 336 in accordance with embodiments of the present invention isshown. The storage controller module 336 includes a storage controller204. In a preferred embodiment, there are two storage controller modules336 in a storage enclosure 112, or no storage controller modules 336 ina JBOD storage enclosure 224. Storage enclosures 112 with no storagecontroller modules 336 are JBOD storage enclosures 224. Storagecontroller module 336 interfaces with chassis midplane 340 throughchassis midplane connector 440.

Referring now to FIG. 4 f, a diagram illustrating chassis 340 and drawer396 midplanes in accordance with embodiments of the present invention isshown. Each drawer 352 has a drawer midplane 396, which is described inmore detail with respect to FIGS. 7 and 8. For engineering debugpurposes, it may be advantageous to provide hard electromechanicalmounting between each drawer midplane 396 and the chassis midplane 340,as shown. However, storage enclosures 112, 224 of the present inventionutilize a cable management system 356 in lieu of hard mounting betweenchassis midplane 340 and each drawer midplane 396.

Referring now to FIG. 4 g, a diagram illustrating a chassis 304 cutawayside view in accordance with embodiments of the present invention isshown. Chassis 304 includes a chassis front surface 320, a chassis rearsurface 324, and a flexible cable chain 360. Power supplies 332 andstorage controller modules 336 are inserted or removed to or from thechassis 304 through the chassis rear surface 324. Drawers 352 areinserted or removed to or from the chassis 304 through the chassis frontsurface 320. In a preferred embodiment, the chassis 304 is two rackunits high.

Referring now to FIG. 5 a, a diagram illustrating a storage enclosure112, 224 in a rack 504 with no drawers 352 extended in accordance withembodiments of the present invention. The storage enclosure 112, 224 ismountable in a standard 19 inch rack 504, using standard mountinghardware at the front left and right corners of the chassis 304 andalong the rear portions of the chassis side surfaces 328. The rack 504includes front rack rails 504 a, 504 b and rear rack rails 504 c, 504 d.When thusly mounted in a rack 504, the storage enclosure 112, 224 is arackmounted storage enclosure 508.

When each of the drawers 352 are fully populated with mounted storagedevices 368, and fully pushed into the chassis 304, the center of mass512 of the rackmounted storage enclosure 508 is generally centeredbetween the left and right sides of the chassis 328 and between thefront rack rails 504 a, 504 b and the rear rack rails 504 c, 504 d.Because the rackmounted storage enclosure 508 center of mass 512 iswithin the confines of the rails of rack 504, there is no moment outsidethe confines of the rack 504 that could contribute to the rack 504tipping over and presenting a safety hazard.

Access to any drawer 352 or mounted storage device 368 is not affectedby vertical position of the rackmounted storage enclosure 508 within arack 504, or the presence or absence of other vertically adjacentstorage enclosures or other modules either above or below therackmounted storage enclosure 508.

Referring now to FIG. 5 b, a diagram illustrating a storage enclosure ina rack 508 with all drawers 352 extended in accordance with embodimentsof the present invention is shown. Each of the drawers 352 are extendedthe predetermined distance 376, which is the maximum distance a drawer352 may be extended from the front surface of the chassis 320.

When each of the drawers 352 are fully populated with mounted storagedevices 368, and fully extended from the chassis front surface 320, thecenter of mass 516 of the rackmounted storage enclosure 508 is generallycentered between the left and right sides of the chassis 328 and isstill between the front rack rails 504 a, 504 b and the rear rack rails504 c, 504 d. Because the rackmounted storage enclosure 508 center ofmass 516 is still within the confines of the rails of rack 504, there isno moment outside the confines of the rack 504 that could contribute tothe rack 504 tipping over and presenting a safety hazard.

The rackmounted storage enclosure 508 presents a safe storage enclosure112, 224 configuration by limiting the weight of the entire storageenclosure 112, 224 and any module within the storage enclosure 112, 224.The power supplies 332 a, 332 b and storage controller modules 336 in apreferred embodiment each weigh less than 4.2 lbs. or 1.9 Kg., and maybe safely serviced by an individual person. The drawers 352 in apreferred embodiment each weigh less than 15 lbs when populated with 162.5 inch disk drive storage devices 208, and may be safely serviced byan individual person. The entire storage enclosure 112, when fullypopulated with two power supplies 332 a, 332 b, two storage controllermodules 336, and three drawers 352 each populated with 16 2.5 inch diskdrive storage devices 208, weighs less than 80 lbs. Storage enclosures224 weigh less than 80 lbs. in the preferred embodiment, since nostorage controller modules 336 are present.

Conventional rackmounted storage enclosures not incorporating thepresent invention in some cases require a single sled containing allmodules of the rackmounted storage enclosure to be extended through thefront surface of the conventional rackmounted storage enclosure in orderto access storage devices. Because of the significant mass of allmodules moved in a forward direction, the center of gravity is shiftedoutside the confines of the conventional rackmounted storage enclosure,thereby creating a forward-tipping moment. This moment may contribute toa tipping danger of the entire rack, which presents a safety hazard.

The rackmounted storage enclosure 508 of the present invention allowsaccess to any mounted storage device 368 in any drawer 352, regardlessof the presence of a wall 520 or similar surface parallel to and againstthe left side or the right side of the rack 504. Furthermore, allmounted storage devices 368 of the rackmounted storage enclosure 508 maybe inserted or removed to or from all drawers 352 of the rackmountedstorage enclosure 508 even if a wall 520 or similar surface is alongboth the left and right sides of the rack 504. Under these conditions,the wall 520 or similar surface projects forward of the rack 504 atleast as far as a fully extended drawer 352. This unique featureprovides side accessibility of any mounted storage device 368 at alltimes—even when the rack 504 is located in a very narrow closet or otherstructure. The present invention includes a left drawer configuration404 in the left drawer 364, and a right drawer configuration 408 in theright drawer 380. This means that all mounted storage devices 368 ineither a left drawer 364 or right drawer 380 are accessed toward thecenter line of the rackmounted storage enclosure 508, and any wall 520as described earlier will not interfere with mounted storage device 368access. Center drawers 372 may have either a left drawer configuration404 or right drawer configuration 408. It is understood that any mountedstorage device 368 of a center drawer 372 may be inserted or removedfrom the center drawer 372 regardless of the presence of any wall 520,since the length of mounted storage devices 368 are less than the widthof a left drawer 364 or right drawer 380.

Referring now to FIG. 6, a block diagram illustrating a storageenclosure 112 in accordance with embodiments of the present invention isshown. Storage enclosure 112 includes two storage controllers 204 a, 204b. However, in JBOD (Just a Bunch of Disks) embodiments, no storagecontrollers 204 a, 204 b are present. When two storage controllers 204a, 204 b are present, they are usually configured as dual redundantstorage controllers where either or both storage controller 204 a, 204 bmay read or write to any storage device 208. In most embodiments,storage controllers 204 a, 204 b include Redundant Array of InexpensiveDisks (RAID) technology to improve performance and protect against theloss of storage devices 208.

Storage controllers 204 a, 204 b include a processor 604 a, 604 b whichexecutes stored programs to control the operations of storagecontrollers 204 a, 204 b and reading/writing data between host computers108 and storage devices 208. Processors 604 a, 604 b include anyprocessing device suitable for use as an embedded processor for storagecontroller 204 a, 204 b, including RISC processors, X86 processors, ARMprocessors, and so on.

For clarity purposes, host I/O controllers are not shown in FIG. 6. HostI/O controllers are part of storage controllers 204 a, 204 b, andinteract with host computers 108 through network 104. Interactionincludes receiving read and write requests from host computers 108 andproviding read data to host computers 108.

Storage controllers 204 a, 204 b also includes memory 608 a, 608 b.Memory 608 a, 608 b includes both volatile and non-volatile memories,and provides storage for stored programs executed by processors 604 a,604 b, write caches, read caches, and other forms of temporary datastorage.

SAS initiators 616 a, 616 b are protocol controllers for the I/O buses220 to storage devices 208 and daisy chain buses 236 to JBOD storageenclosures 224. In the preferred embodiment, SAS initiators 616implement the Serial Attached SCSI (SAS) protocol. In the preferredembodiment, SAS initiators 616 are SAS2008 “Falcon” devices from LSILogic, Inc. In other embodiments, SAS initiators 616 a, 616 b are FibreChannel, SSA, or SATA protocol controllers—or any other I.O interfacesuitable for connection to storage devices 208.

SAS initiators 616 a, 616 b are coupled to SAS root expanders 612 a, 612b in order to provide SAS I/O signaling to each of the drawers 352 orexpansion JBOD storage enclosures 224 controlled by storage controllers204 a, 204 b. In non-SAS embodiments, SAS root expanders 612 a, 612 bmay instead be hubs or switches to perform a similar I/O bus expansionfunction. SAS root expanders 612 a, 612 b provide independentcommunication paths 220 to one side of each drawer 352, and as daisychain bus 236 a, 236 b to an expansion JBOD storage enclosure 224. Inthe preferred embodiment, SAS root expanders 612 a, 612 b are PMC PM8005devices manufactured by PMC-Sierra. In other embodiments, SAS rootexpanders 612 a, 612 b are different devices than PMC PM8005 devices.SAS root expanders 612 a, 612 b also provide an alternate communicationpath to the other storage controller 204 a, 204 b to continue to provideaccess to storage devices 208 in the event of certain failures. Forexample, if SAS root expander 612 a fails, SAS initiator 616 a may stillcommunicate with storage devices 208 by communicating through SAS rootexpander 612 b.

FIG. 6 illustrates three drawers 352: drawer 0 352 a, drawer 1 352 b,and drawer 2 352 c. Each drawer 352 a, 352 b, 352 c of the preferredembodiment includes up to 16 storage devices 208. However, a givendrawer 352 may include any number of storage devices 208. Storagedevices 208 each include two communication paths, which are each routedto a different SAS expander 212 on the drawer midplane 396.

Each SAS expander 212 is routed to a different bus 220 and SAS rootexpander 612. In the preferred embodiment, SAS expanders 212 arePMC-Sierra PM8004 devices. In other embodiments, SAS expanders 212 aredifferent devices than PMC PM8004 devices. The two communication pathsto each storage device 208 provide redundancy to each storage device forgreater communication availability, and in some cases higher performanceby increasing the communication bandwidth to storage devices 208.

In embodiments where more data storage is required than is normallyprovided by a single storage enclosure 112, an expansion storageenclosure, or JBOD storage enclosure 224, is provided. Daisy chain buses236 provide high-bandwidth data transfers to and from SAS expanders 212in JBOD storage enclosures 224.

Referring now to FIG. 7, a block diagram illustrating a drawer midplane396 in accordance with embodiments of the present invention is shown.The drawer midplane 396 provides interconnection between storage devices208, drawer 352 electronics, and DC and signal cables within the cablemanagement system 356.

Drawer midplane 396 communicates with SAS root expanders 612 a, 612 bthrough SAS buses 220 and SAS expanders 212 a, 212 b, respectively. SASexpanders 212 a, 212 b each communicate with storage devices 208 in thedrawer 352 through SAS connections 716 a, 716 b, where an independentSAS connection 716 is provided to each storage device 208 from each SASexpander 212 a, 212 b. An I²C bus 720 is provided between SAS expanders212 a, 212 b in order to communicate between SAS expanders 212.

Drawer midplane 396 includes independent control logic 708 a, 708 b,which communicates storage device status 724 to and from each storagedevice 208, memory 704 a, 704 b, and SAS expanders 212 a, 212 b.

Memories 704 a, 704 b store execution code, configuration data, andmanagement data for each drawer 352, and include flash and static RAM(SRAM) devices. SAS expanders 212 access memory devices 704 a, 704 bfrom their respective expansion buses in the drawers 352.

Finally, drawer midplane 396 includes temperature sensors 712 a, 712 b.Temperature sensors 712 a, 712 b measure the ambient temperature of thedrawer midplane 396. SAS expanders 212 a, 212 b read the temperaturesensors 712 a, 712 b, respectively, and report the ambient temperatureto the processor 604 a, 604 b. In some embodiments, the processors 604a, 604 b change fan speed of fans in the power supplies 332 a, 332 b orelsewhere in chassis 304 in response to changes in ambient temperature.

Referring now to FIG. 8, a block diagram illustrating a drawer 352interconnection to a storage enclosure 112, 224 in accordance withembodiments of the present invention is shown. Drawer 352 includesdrawer midplane 396, which was described with reference to FIG. 7.Drawer midplane 396 communicates directly with the chassis midplane 340through an interconnect cable assembly 828 of the cable managementsystem 356. The interconnect cable assembly 828 includes power andsignal cables required by the drawer midplane 396 and storage devices208 within the drawer.

The drawer midplane 396 includes drawer indicators and controls 424. Inone embodiment, drawer indicators and controls 424 includes a pushbutton804, which allows a user to indicate to the processors 604 a, 604 b thateither a user desires to remove a drawer 352 from the chassis 304(through remove drawer request 820), or a drawer 352 has been installedto the chassis 304 and is ready to be made online to the storageenclosure 112, 224. In a preferred embodiment, pushbutton 804 is notpresent within drawer indicators and controls 424, and instead a userprovides such an indication through GUI 120 of management computer 116.

Drawer indicators and controls 424 also include one or more indicators808. In the preferred embodiment, an indicator 808 is provided on thefront of drawer 352 to indicate a drawer 352 is safe to remove from thechassis 304. The indicator 808 is driven by a remove drawer indicator824 signal from the chassis midplane 340. Other indicators 808 may bepresent within drawer midplane 396, including a drawer fault indicator,storage device 208 fault indicators, or other indicators associated withdrawer 352 or drawer midplane 396.

Interconnect cable assembly 828 includes DC power 816. DC power 816 isprovided by power supplies 332 a, 332 b and includes various grounds andDC voltages required by storage devices 208 and drawer midplane 396. Inthe preferred embodiment, DC voltages 816 include ground, +5 Volts DC,and +12 Volts DC. However, in other embodiments other DC voltages 816may be present.

Interconnect cable assembly 828 also includes a drawer present 812signal, which indicates to the chassis midplane 340 that a drawer 352 ispresent and interconnected to the chassis midplane 340 through theinterconnect cable assembly 828. In the preferred embodiment, the drawerpresent 812 signal is simply a grounded signal when the drawer 352 isinterconnected. In other embodiments, drawer present 812 is a serialbitstream or predetermined DC voltage that indicates the presence andpossibly the status of drawer 352.

Interconnect cable assembly 828 also includes SAS data buses 220, whichprovide redundant bidirectional data communication between the drawermidplane 396 and each storage controller 204 a, 204 b. Electricalfailures in any one drawer 352 or between any one drawer 352 and thechassis midplane 340 do not affect any other drawer 352. Electricalfailures include a loss of DC power 816 to a drawer 352 or a shorted ordisconnected signal in interconnect cable assembly 828.

Referring now to FIG. 9, a block diagram illustrating storage enclosure112, 224 DC power distribution in accordance with embodiments of thepresent invention is shown. The power distribution arrangementillustrated in FIG. 9 prevents a power failure in any module fromaffecting any other module of the storage enclosure 112, 224. Modulesinclude drawers 352, power supplies 332, or storage controller modules336.

FIG. 9 illustrates a storage enclosure 112 with three drawers 352,identified as drawers 352 a, 352 b, and 352 c. The storage enclosure 112has two storage controllers 204 a and 204 b, and two power supplies 332a and 332 b. Each drawer 352 stores up to a predetermined number ofstorage devices 208, although a given drawer 352 at times may contain nostorage devices 208. The power supplies 332 a, 332 b each has anindependent connection to external AC or DC power 336, and a singlepower supply 332 a, 332 b in some embodiments is able to power theentire storage enclosure 112, 224. Each of the modules (drawers 352 a,352 b, and 352 c, storage controllers 204 a, 204 b, or power supplies332 a, 332 b) are interconnected through the chassis midplane 340, whichis illustrated with a dashed line for clarity.

Each module has an associated energy storage capacitor C1-C7 as anessential part of that module. In a preferred embodiment, the energystorage capacitors C1-C7 are nominally 4000 uF. However, other capacitorC1-C7 values may be used in order to meet the timing requirementdescribed below. The line connecting all the modules to the chassismidplane 340 could be either 5 volt DC or 12 volt DC, or any other DCvoltage or combination of DC voltages. Where multiple DC voltages areprovided to each of the modules by the power supplies 332 a, 332 b,separate power distribution circuits are provided for each DC voltage,and the circuit is identical for each separate DC voltage.

Each power supply 332 a, 332 b and storage controller 204 a, 204 b has adiode D4-D7 placed between the energy storage capacitor C4-C7 and the DCvoltage. For the drawers 352 a, 352 b, and 352 c, this diode D1-D3 is onthe chassis midplane 340 while for the storage controllers 204 a, 204 band power supplies 332 a, 332 b the diode D4-D7 is part of that module.The diodes D1-D7 isolate each energy storage capacitor C1-C7 from the DCvoltage.

To explain in more detail one needs to consider how a short in one ofthe modules affects the common rail and the energy stored in the all theother energy storage capacitors C1-C7. For this explanation, the shortcan be considered to occur in one of the energy storage capacitors C1-C7itself. The behavior is slightly different for the drawers 352 a, 352 b,and 352 c and storage controllers 204 a, 204 b than for the powersupplies 332 a, 332 b.

First, consider a short in C6 908 a associated with power supply 332 a.Although the voltage immediately goes to zero at C6, the voltage railand all the remaining energy in storage capacitors C1-C5, and C7 areunaffected. C1-C5, and C7 are unaffected since they are isolated by thediode D6 904 a in power supply 332 a, which becomes reverse biased anddoes not allow energy from any of the remaining capacitors C1-C5, and C7to flow into the short. The power supply 332 a itself dumping energyinto its shorted capacitor C6 908 a does not need to be considered sincethe power supply 332 a in most embodiments has protective circuits whichshut it down once the short is sensed. This action of the circuit inresponse to a short in the power supply 332 itself, is used in allpractical redundant power supply configurations.

Next consider a short in the drawer 352 a, or more specifically, energystorage capacitor C1 924 a. At the moment this short occurs, the commonvoltage rail is pulled to zero volts as a result of the short in C1 924a. Although the power supplies 332 a, 332 b will dump energy into thisshort, the diodes D2 932 b and D3 932 c associated with the otherdrawers 352 b and 352 c, respectively, become reverse biased and preventthe energy that is stored in their associated capacitors C2 924 b and C3924 c, respectively, from flowing back onto the voltage rail and intothe short. Their energy will flow instead into storage devices 208 andstorage controllers 204 a, 204 b and allow these modules to continue tooperate for a period of time until the voltage level falls below somecritical threshold. Meanwhile, at the shorted capacitor C1 924 a, bothpower supplies 332 a, 332 b are dumping energy (current) into the shortwhich will cause fuse F1 928 a to open. Once this happens, the voltagerail will return to its normal level and recharge the energy storagecapacitors C2-C7 in the remaining elements.

In order to provide proper fault isolation, there is a critical timingparameter which must be met. The time for fuse F1 928 a to open must beshorter than for the voltage levels in the capacitors C2 and C3associated with drawers 352 b and 352 c, and capacitors C4 920 a and C5920 b associated with controllers 204 a, 204 b, respectively, to reachthe critical level where their circuits can no longer function. In apreferred embodiment, fuses F1-F5 use electronic circuits such asTPS24720 controllers with IRF6718 FETs (field effect transistors)instead of actual fuses to shorten this fault time to 1 millisecond orless, but the principle is the same in either case. FETs such as RenesasUPA2766T 1A devices configured as diodes instead of actual diodes D1-D7may be used to reduce the forward voltage loss but again the action isthe same as if a real diode was used. In embodiments using actualdiodes, devices similar to 19TQ015 are used. In the preferredembodiment, a TPS2419 ORing FET controller is used, which makes a FETbehave like a diode but has lower forward voltage loss. With anelectronic fuse there is some control over the timing parameter, whereasif an actual fuse was used the trip time might be longer, such as 10 ms.

Electronic fuses may be set to retry automatically, or they may beconfigured to wait for a power cycle of storage enclosure 112, 224. Inthe preferred embodiment, a software-controlled power cycle sequence ispreferred, since repeatedly running into an overcurrent trip cycle canbe very damaging to electronic components.

In the preferred embodiment, a storage controller 204 separately enablesindependent DC power to each drawer 352 under software control. In otherembodiments, a processor or other circuitry on the chassis midplane 340separately enables independent DC power to each drawer 352 undersoftware control. In yet other embodiments, a processor or othercircuitry on the chassis midplane 340 separately enables independent DCpower to each drawer 352 under manual control such as through apushbutton on the storage enclosure 112, 224.

Referring now to FIG. 10 a, a flowchart illustrating a drawer 352installation process of the present invention is shown. Drawers 352 areinserted as part of adding a storage enclosure 112, 224 to an equipmentrack, expanding the storage capacity of a storage enclosure 112, 224, orafter servicing one or more components in a drawer 352. Storage devices208 are normally individually removed or inserted in a drawer 352, asdescribed with reference to FIG. 3 j. Flow begins at block 1004.

At block 1004, power to the drawer 352 is inactivated. In oneembodiment, a mechanical switch removes power from an interconnect cableassembly 828 between the storage enclosure 112 and the drawer 352. In apreferred embodiment, the user uses a GUI 120, command line interface,or other software-based mechanism to command the storage enclosure 112to remove power from the drawer 352. Flow proceeds to block 1008.

At block 1008, the user mechanically installs the drawer 352 on drawerslides 348 of the storage enclosure 112, 224. In some embodiments, theuser engages a mechanical latch on the drawer bottom 416 in order tosecure the drawer 352 to drawer slides 348 of the storage enclosure 112,224. The mechanical latch on the drawer bottom 416 engages a mechanicallatch hole 350 on the drawer slides 348. Flow proceeds to block 1012.

At block 1012, the user mechanically attaches a cable management system356, if present, to the drawer 352. The cable management system 356protects electrical wiring between the storage enclosure 112, 224 andeach drawer 352. The cable management system 356 moves with aninterconnect cable assembly 828 as the drawer 352 is extended orretracted. In some embodiments, the cable management system 356 is onlymechanically connected at the drawer 352 end. In other embodiments, thecable management system 356 is mechanically connected at both the drawer352 end and the storage enclosure 112, 224 end. Flow proceeds to block1016.

At block 1016, the user attaches the interconnect cable assembly 828 tothe drawer midplane 396. This step electrically connects the drawer 352to the storage enclosure 112, 224. Flow proceeds to block 1020.

At block 1020, a user requests the drawer 352 be brought online to thestorage enclosure 112, 224. In one embodiment, the drawer 352 has apushbutton or other control 804 that generates a signal 820 to thestorage enclosure 112, 224. In a preferred embodiment, the user uses aGUI 120, command line interface, or other software-based mechanism torequest the drawer 352 be brought online. Flow proceeds to block 1024.

At block 1024, the storage controller 112, 224 detects drawer presence.In a preferred embodiment, the interconnect cable assembly 828 between adrawer 352 in the storage enclosure 112, 224 includes a wire or signal812 having a predetermined DC state when the drawer 352 isinterconnected to the storage enclosure 112, 224. In one embodiment, thepredetermined DC state is grounded. In a second embodiment, thepredetermined DC state is a predetermined DC voltage level such as 3.3Volts DC or 5 Volts DC. In other embodiments, the drawer 352 transmits apredetermined serial bitstream or parallel communications message 812 tothe storage enclosure 112, 224. The bitstream or parallel communicationsmessage 812 identifies the presence of the drawer 352, and in someembodiments an indication of a specific identity of a drawer 352differentiated from specific identities of other drawers 352. In yetother embodiments, optical sensing is supported within the storageenclosure 112, 224 to determine the presence of each drawer 352. Flowproceeds to block 1028.

At block 1028, the storage controller 112, 224 applies power to thedrawer 352 through the interconnect cable assembly 828. The DC outputsof the power supplies 332 a, 332 b in the storage enclosure 112, 224 arecontrolled by the storage controllers 204 a, 204 b in order toselectively provide DC power to each drawer 352. Once power is appliedto a drawer 352, all storage devices 208 in the drawer 352 areactivated. Flow proceeds to block 1032.

At block 1032, the storage controller 204 a, 204 b brings the drawer 352online. Bringing the drawer 352 online includes initializing drawermidplane 396 components and each storage device 208 in the drawer 352.Storage devices 208, where present, in many embodiments are built intoRAID logical volumes. Once the drawer 352 is online, all storage devices208 in the drawer 352 are able to be accessed. Flow ends at block 1032.

Referring now to FIG. 10 b, a flowchart illustrating a drawer 352removal process of the present invention is shown. Drawers 352 areremoved in order to service drawer 352 components or assemblies otherthan storage devices 208, including the drawer midplane 396 or theinterconnect cable assembly 828 interconnecting a drawer 828 with thestorage enclosure 112, 224. Storage devices 208 are normallyindividually removed or inserted, as described with reference to FIG. 3j. Flow begins at block 1036.

At block 1036, the storage controllers 204 a, 204 b detect drawer 352presence. In a preferred embodiment, the interconnect cable assembly 828between a drawer 352 in the storage enclosure 112, 224 includes a wireor signal having a predetermined DC state 812 when the drawer 352 isinterconnected to the storage enclosure 112, 224. In one embodiment, thepredetermined DC state is grounded. In a second embodiment, thepredetermined DC state is a predetermined DC voltage level such as 3.3volts DC or 5 volts DC. In other embodiments, the drawer 352 transmits apredetermined serial bitstream or parallel communications message 812 tothe storage enclosure 112, 224. The bitstream or parallel communicationsmessage 812 identifies the presence of the drawer 352, and in someembodiments an indication of a specific identity of a drawer 352differentiated from specific identities of other drawers 352. In yetother embodiments, optical sensing is supported within the storageenclosure 112, 224 to determine the presence and/or absence of eachdrawer 352. Flow proceeds to block 1040.

At block 1040, a user requests the drawer 352 be taken off-line to thestorage enclosure 112, 224. In one embodiment, the drawer 352 has apushbutton or other control 804 that generates a signal 820 to thestorage enclosure 112, 224. In a preferred embodiment, the user uses aGUI 120, command line interface, or other software-based mechanism toselect the drawer 352 be taken off-line. Flow proceeds to block 1044.

At block 1044, the storage controllers 204 a, 204 b check for storageredundancy. Storage redundancy is important in order to prevent dataloss during the act of taking a drawer 352 off-line. Storage redundancyprovides data redundancy across the storage device drawers 352 of thestorage enclosure 112, 224, such that if any one drawer 352 is removedor nonfunctional, data on the storage devices 208 of the removed drawer352 may be found or re-created from other storage devices 208 in othernon-removed drawers 352. Flow proceeds to decision block 1048.

At decision block 1048, the storage controllers 204 a, 204 b determineif the data stored in the drawer 352 to be taken off-line is redundant.If the storage controllers 204 a, 204 b determine that the data storedin the drawer 352 to be taken off-line is not redundant, then flowproceeds to block 1052. If the storage controllers 204 a, 204 bdetermine that the data stored in the drawer 352 to be taken off-line isredundant, then flow proceeds to block 1060.

At block 1052, the storage controllers 204 a, 204 b notify the user thatthe data in the drawer 352 to be taken off-line is not redundant. Flowproceeds to block 1056.

At block 1056, the user corrects the data redundancy deficiency of thestorage enclosure 112, 224. In one embodiment, the user redistributesdata according to well-known redundant array of inexpensive disks (RAID)techniques across the storage device drawers 352 in order to make thedata on the drawer 352 to be taken off-line redundant. Flow proceeds todecision block 1048.

At block 1060, the storage controllers 204 a, 204 b remove power fromthe drawer 352. The DC outputs of the power supplies 332 a, 332 b in thestorage enclosure 112, 224 are controlled by the storage controllers 204a, 204 b in order to selectively provide DC power to each drawer 352.Once power is removed from a drawer 352, all storage devices 208 in thedrawer 352 are inactivated. The storage controllers 204 a, 204 b areprepared for all storage devices 208 in the drawer 352 beinginactivated, and because storage redundancy has previously been assured,the storage controllers 204 a, 204 b remove power from the drawer 352without concern for data loss. Flow proceeds to block 1064.

At block 1064, the storage controllers 204 a, 204 b activate a drawerindicator 808 to remove the drawer 352. In a preferred embodiment, thedrawer indicator 808 is included within drawer indicators and controls424, and is an LED on the front of the drawer 352 which indicates to auser that the drawer 352 is able to be safely removed from the storageenclosure 112, 224. In another embodiment, the drawer indicator 808 is atext display on the front of the drawer 352 which instructs the user toremove the drawer 352 from the storage enclosure 112, 224. In yetanother embodiment, the drawer indicator is an indicator in a managementcomputer GUI 120 which instructs the user to remove the drawer 352 fromthe storage enclosure 112, 224. Flow proceeds to block 1068.

At block 1068, the user mechanically detaches the cable managementsystem 356, if present, from the drawer 352. The cable management system356 protects electrical wiring between the storage enclosure 112, 224and each drawer 352. In some embodiments, the cable management system356 is only mechanically disconnected at the drawer 352 end. In otherembodiments, the cable management system 356 is mechanicallydisconnected at the drawer 352 end and the storage enclosure 112, 224end. Flow proceeds to block 1072.

At block 1072, the user detaches the interconnect cable assembly 828from the drawer midplane 396. This step electrically disconnects thedrawer 352 from the storage enclosure 112, 224. Flow proceeds to block1076.

At block 1076, the user mechanically removes the drawer 352 from drawerslides 348 of the storage enclosure 112, 224. In some embodiments, theuser engages a mechanical latch on the drawer bottom 416 in order toremove the drawer 352 from the drawer slides 348 of the storageenclosure 112, 224. The mechanical latch on the drawer bottom 416engages a mechanical latch hole 350 on the drawer slides 348. Flow endsat block 1076.

Referring now to FIG. 11 a, a diagram illustrating a mounted storagedevice 368 of the present invention is shown. The mounted storage device368 includes three components: the storage device 208 itself, a storagedevice carrier left side 1104, and a storage device carrier right side1108. Each of the storage device carrier left side 1104, and right side1108 include suitable fasteners to attach each of the storage devicecarrier left 1104 and right 1108 sides to the storage device 208.

The storage device carrier left side 1104 includes a left side halffinger grab 1112, and the storage device carrier right side 1108includes a right side half finger grab 1116. The left side half fingergrab 1112 and the right side half finger grab 1116 together providesurfaces through which a user achieves finger purchase of a mountedstorage device 368 when inserting or removing a mounted storage device368 to/from a drawer 352. The mounted storage device 368 is removed froma drawer 352 by pinching the left side half finger grab 1112 and theright side half finger grab 1116 together in a direction of fingerpressure to disengage the carrier latch 1316, and pulling the mountedstorage device 368 from the drawer 352.

Referring now to FIG. 11 b, a stack of four mounted storage devices 368of the present invention is shown. Although four mounted storage devices368 are illustrated in FIG. 11 b, the present invention is not limitedto four mounted storage devices 368 in a stack, and a stack may containone or more mounted storage devices 368. Additionally, not all storagedevice spaces in a stack may be populated with a mounted storage device368. For example, there may be mounted storage devices 368 in the middletwo mounted storage device slots in a stack, and the top and bottommounted storage device slots in the stack may be empty.

Referring now to FIG. 12 a, a diagram illustrating a front view of astorage device carrier left side 1104 in accordance with embodiments ofthe present invention is shown. The storage device carrier left side1104 includes a side portion 1216 and a front portion 1220. The sideportion 1216 has attachment holes 1204 for securing a storage device 208to the storage device carrier left side 1104. The attachment holes 1204are used in conjunction with screws or other suitable fasteners. Thefront portion of the storage device carrier left side 1220 includes aleft side half finger grab 1112, and is shaped in order to allow a userfingertip to exert horizontal force toward the center of a mountedstorage device 368.

In some embodiments, the storage device carrier left side 1104 includesa stiff portion 1208 that resists deflection when a user fingertipexerts horizontal force toward the center of a mounted storage device368. Also in some embodiments, the storage device carrier left side 1104includes an alignment tab recess 1212. The alignment tab recess 1212receives an alignment tab 1312 of the storage device carrier right side1108 in order to maintain alignment between the storage device carrierleft side 1104 and right side 1108 when the finger grabs 1112, 1116 arepushed together. In some embodiments, the alignment tab recess 1212 andalignment tab 1312 are not present.

Referring now to FIG. 12 b, a diagram illustrating a rear view of thestorage device carrier left side 1104 in accordance with embodiments ofthe present invention is shown. The rear view of the storage devicecarrier left side 1104 further illustrates the features described withrespect to FIG. 12 a.

Referring now to FIG. 13 a, a diagram illustrating a front view of astorage device carrier right side 1108 in accordance with embodiments ofthe present invention is shown. The storage device carrier right side1108 includes a side portion 1320 and a front portion 1324. The sideportion 1320 has attachment holes 1304 for securing a storage device 208to the storage device carrier right side 1108. The attachment holes 1304are used in conjunction with screws or other suitable fasteners. Thefront portion of the storage device carrier right side 1324 includes aright side half finger grab 1116, and is shaped in order to allow a userfingertip to exert horizontal force toward the center of a mountedstorage device 368.

The storage device carrier right side 1108 includes a carrier latch1316, which is a ramped projection that engages a latching hole 436 ofthe drawer chassis 388 to secure the mounted storage device 368 when itis fully seated. The ramped surface toward the rear of the carrier latch1316 allows the front portion of storage device carrier right side 1324to deflect inwardly as the mounted storage device 368 is being seated inthe drawer chassis 388.

In some embodiments, the side portion of storage device carrier rightside 1320 includes a flexible portion 1308 that allows deflection when auser fingertip exerts horizontal force on the right side half fingergrab 1116 toward the center of a mounted storage device 368. Also insome embodiments, the front portion of storage device carrier right side1324 includes an alignment tab 1312. The alignment tab 1312 engages analignment tab recess 1212 of the front portion of the storage devicecarrier left side 1220 in order to maintain alignment between thestorage device carrier left side 1104 and right side 1108 when thefinger grabs 1112, 1116 are pushed together. In some embodiments, thealignment tab recess 1212 and alignment tab 1312 are not present.

Referring now to FIG. 13 b, a diagram illustrating a rear view of thestorage device carrier right side 1108 of embodiments of the presentinvention is shown. The rear view of the storage device carrier rightside 1108 further illustrates the features described with respect toFIG. 13 a.

Although FIGS. 13 a and 13 b illustrate the carrier latch 1316, flexibleportion 1308, and alignment tab 1312 on the storage device carrier rightside 1108, and the stiff portion 1208 and alignment tab recess 1212 onthe storage device carrier left side 1104, it should be understood byone of ordinary skill in the art that these features may be locatedopposite to what is shown. That is, the carrier latch 1316, flexibleportion 1308, and alignment tab 1312 on the storage device carrier leftside 1104, and the stiff portion 1208 and alignment tab recess 1212 onthe storage device carrier right side 1108.

In a preferred embodiment, the storage device carrier left side 1104 andright side 1108 are each fabricated as a single piece from a costeffective resilient material such as ABS plastic. In other embodiments,either or both the storage device carrier left side 1104 and right side1108 are each fabricated as multiple pieces of material. In someembodiments, different materials may be used for each piece of a storagedevice carrier left side 1104 and right side 1108. In other embodiments,similar or the same materials may be used for each piece of a storagedevice carrier left side 1104 and right side 1108. Materials used tofabricate the storage device carrier left side 1104 and right side 1108includes various plastics or metals such as aluminum, steel, or alloys.

Finally, those skilled in the art should appreciate that they canreadily use the disclosed conception and specific embodiments as a basisfor designing or modifying other structures for carrying out the samepurposes of the present invention without departing from the spirit andscope of the invention as defined by the appended claims.

I claim:
 1. A storage enclosure, comprising: a chassis; and a plurality of drawers, the plurality of drawers each comprising up to a predetermined number of storage devices; wherein the plurality of drawers are individually extendable up to a predetermined distance through a front surface of the chassis, wherein when each drawer of the plurality of drawers comprises the predetermined number of storage devices and is extended the predetermined distance through the front surface of the chassis, the center of mass of the storage enclosure is behind the front surface of the chassis.
 2. The storage enclosure of claim 1, wherein the storage enclosure is rackmountable, wherein access to any drawer or storage device is not affected by vertical position of the storage enclosure within a rack or other modules or storage enclosures vertically adjacent to the storage enclosure, wherein no storage devices are accessed from the top or bottom of a drawer.
 3. The storage enclosure of claim 2, wherein the storage enclosure is 2 rack units high, wherein access to any storage device in a drawer is not affected by horizontal proximity of the storage enclosure to a wall surface parallel to a side surface of the storage enclosure.
 4. The storage enclosure of claim 3, wherein all storage devices in any drawer of the plurality of drawers are inserted or removed through a common side of the drawer, wherein any storage device may be inserted or removed from any drawer of the plurality of drawers even if the closest side surface of the chassis is parallel to and in contact with a wall.
 5. The storage enclosure of claim 1, the storage enclosure further comprising one or more power supplies and one or more storage controllers, wherein the one or more power supplies and the one or more storage controllers are individually insertable and removable through a rear surface of the chassis.
 6. The storage enclosure of claim 5, wherein the one or more storage controllers perform storage enclosure redundancy checks before allowing a user to disconnect and remove any drawer of the plurality of drawers.
 7. The storage enclosure of claim 6, redundancy checks comprising verifying that user data stored on storage devices of the plurality of drawers will not be lost if a user disconnects any drawer of the plurality of drawers.
 8. The storage enclosure of claim 7, wherein disconnects comprises disconnecting any of a DC power cable and a signal cable between a drawer and a chassis midplane.
 9. The storage enclosure of claim 5, wherein no top level access is required to the storage enclosure to remove or insert a drawer, a storage device, a power supply, and a storage controller.
 10. The storage enclosure of claim 9, wherein the predetermined number of storage devices is 16, wherein each drawer of the plurality of drawers weighs less than 20 lbs when 16 storage devices are mounted in each drawer.
 11. The storage enclosure of claim 10, the storage enclosure comprising two power supplies, two storage controllers, and three drawers, wherein the storage enclosure weighs less than 80 lbs when 16 storage devices are mounted in each drawer.
 12. The storage enclosure of claim 11, wherein each drawer is electrically and mechanically removable from the chassis after the drawer is extended the predetermined distance from the front of the chassis, wherein each drawer is electrically and mechanically removable from the chassis without requiring top level access to the drawer or the storage enclosure, wherein each drawer is electrically and mechanically removable from the chassis without requiring tools.
 13. The storage enclosure of claim 1, further comprising a cable management system between each drawer and the storage enclosure, wherein the cable management system protects an interconnect cable assembly between each drawer and the storage enclosure from being damaged when the drawer is extended from or pushed into the chassis.
 14. The storage enclosure of claim 13, wherein the cable management system is linearly movable in a forward direction as the drawer is extended from the chassis and a rearward direction as the drawer is retracted into the chassis, wherein the cable management system limits sideways movement of the interconnect cable assembly when the drawer is extended or retracted.
 15. The storage enclosure of claim 14, wherein a failure of any of a drawer, a DC power cable, and a signal cable does not affect the operation of any other drawer of the plurality of drawers or any storage device in any other drawer of the plurality of drawers.
 16. The storage enclosure of claim 15, wherein when any drawer of the plurality of drawers is extended from the chassis, no AC power is directly user accessible in the drawer or the chassis.
 17. The storage enclosure of claim 1, wherein when each drawer of the plurality of drawers comprises the predetermined number of storage devices and is extended the predetermined distance through the front surface of the chassis, the center of mass of the storage enclosure is between the front surface and the rear surface of the chassis.
 18. The storage enclosure of claim 17, wherein the storage enclosure is mounted in a 19″ rack, wherein the storage enclosure center of mass is within the envelope of front and rear rack rails when each drawer of the plurality of drawers comprises the predetermined number of storage devices and is extended the predetermined distance through the front surface of the chassis.
 19. A storage enclosure for safe mounting in a 19″ rack, the storage enclosure comprising: one or more drawers of a left drawer configuration, wherein the one or more drawers of the left drawer configuration allow storage devices to be inserted or removed only from the right side of the drawer; one or more drawers of a right drawer configuration, wherein the one or more drawers of the right drawer configuration allow storage devices to be inserted or removed only from the left side of the drawer; one or more storage controller modules, each of the one or more storage controller modules comprising a storage controller for controlling one or more storage devices of the one or more drawers of the left drawer and right drawer configuration; and one or more power supplies, wherein the one or more power supplies provide DC power to the one or more drawers of the left drawer and right drawer configuration and the one or more storage controller modules, wherein when each of the drawers of the left drawer and right drawer configurations are fully populated with storage devices and is fully extended from the front surface of the chassis, the center of mass of the storage enclosure is between the front surface and the rear surface of the chassis.
 20. The storage enclosure of claim 19, wherein each of the drawers of the left drawer and right drawer configurations weigh less than 20 lbs when fully populated with sixteen storage devices per drawer, wherein the storage enclosure weighs less than 80 lbs when two power supplies, two storage controller modules, and three drawers fully populated with sixteen storage devices per drawer are installed in the storage enclosure. 